Modified impedance tube measurements and energy dissipation inside absorptive materials

Author: Leping Feng

Abstract:
Impedance tube is an important tool to measure acoustic properties of a material, for which two methods have been standardized. The methods for a ‘‘modified’’ impedance tube have been developed recently to measure material properties in the condition of an anechoic termination. Instead of commonly used twoload or two-source methods, a method with direct and inverted configuration in cooperation with the single-microphone method is suggested in this paper. With the help of transfer matrix method, combined effect of several materials placed in series can be predicted from individual properties. A simple recurrence formula is obtained to relate the acoustic properties of a multilayer structure with the reflection and transmission coefficients of each layer. Very good agreements are obtained between the prediction and the direct measurements. Energy dissipations inside porous materials for different situations are studied and compared.

Keywords:
Sound absorption
Impedance tube
Scattering matrix
Transfer matrix method
Direct and inverted configurations

Published in: Applied Acoustics (Volume 74, Issue 12,  December  2013)

Publisher: Elsevier

ISSN Information: 0003-682X

Modified impedance tube measurements and energy dissipation inside absorptive materials

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